This invention relates generally to the field of photographic printing and more particularly to a method and apparatus for photographic exposure in a printer utilizing a liquid crystal display (LCD) pad.
In conventional photographic printing, a negative is typically scanned by a light sensor, such as a charge coupled device, which measures the light transmitted through various locations of the negative. Densitometric information from the negative is processed, converted and eventually fed to an exposure control computer which calculates the exposure by computing average red, green and blue exposure levels for the entire image. The computer controls a light source, typically a lamp house, including a shutter and light subtractive filtering means. The negative is positioned at a print station located between the light source and the photosensitive paper thereby allowing light to pass through the negative to produce the proper image on the photosensitive paper. The computer begins the exposure process by activating the light source and controlling the exposure time for the red, green and blue colors. If exposure for a certain color has occurred for the calculated period of time, the computer controls a light subtractive, or additive filter which is placed within the light path to cease, or commence exposure of a specific color. After the exposure time for each of the red, green and blue colors has expired, the print is fully developed.
One disadvantage to the conventional photographic exposure technique, is that the exposure level (time, intensity or a combination of both) for each color is the same throughout the entire negative regardless of the variation in densities within the negative. Since it has not been possible to vary the exposure level to accommodate different densities at locations within the negative, the exposure control computer calculates an average exposure time for each color of light. This may affect the quality of the exposure, especially when different locations on the negative contain different density or transmittance levels. In this situation, an unbalanced exposure may be created resulting in a print containing locations which are overly dark and/or overly light. This often occurs when a scene contains a background which is either darker or lighter than the foreground; for example, when a dark subject is located in the middle of a light background which surrounds the subject, or vice versa.
Conventional photographic exposure systems are not capable of initiating different exposure levels for individual locations on the negative (i.e., the background and the foreground). An average exposure time for the entire image scene on the negative is calculated based upon the transmittance and density levels of individual locations. Using a uniform intensity lamp, the exposure levels across the entire print cannot be varied to accommodate for different density levels throughout the negative because the duration of the light is uniform throughout the entire negative. As a result, the proper contrast between the background and foreground is not obtained thereby impairing the quality of the exposed print.
It is therefore an object of the present invention to provide a method and apparatus for creating an image onto a photosensitive medium which is capable of varying the exposure level at different areas of the photosensitive medium to accommodate for extreme variations in density on the negative.
It is also an object of the present invention to provide method and apparatus for creating an image onto a photosensitive medium which contains a more accurate representation of contrast within the imaged scene.
It is also an object of the present invention to provide a method and apparatus for creating an image onto a photosensitive medium which alleviates the necessity for calculating average density levels and exposure times for different colors within the image.
It is also an object of the present invention to provide a method and apparatus for creating an image onto a photosensitive medium which is capable of varying the exposure level at different areas of the photosensitive medium by varying area exposure times.